In many wireless communication systems, a frame structure is used for data transmission between a transmitter and a receiver. For example, the IEEE 802.11 standard uses frame aggregation in a Media Access Control (MAC) layer and a physical (PHY) layer.
FIG. 1 shows a general framing structure 10 for a wireless communication system including one or more transmitters and one or more receivers. In a typical transmitter, a MAC layer receives a MAC Service Data Unit (MSDU) 11 from an upper layer and attaches a MAC header 12 thereto, in order to construct a MAC Protocol Data Unit (MPDU) 13. The MAC header 12 includes information such as a source address (SA) and a destination address (DA). The MPDU 13 is a part of a PHY Service Data Unit (PSDU) 14 and is transferred to a PHY layer in the transmitter to attach a PHY header 16 thereto to construct a PHY Protocol Data Unit (PPDU) 18. The PHY header 16 includes parameters for determining a transmission scheme including a coding/modulation scheme. Further, before transmission as a packet from a transmitter to a receiver, a training sequence 19 is attached to the PPDU 18, wherein the training sequence 19 can include channel estimation and synchronization information. The PHY header 16 and the training sequence 19 form a PHY preamble 17.
Most wireless communication protocols include a retransmission mechanism to combat data errors due to fading channels. Existing retransmission mechanisms include stop-and-wait retransmission, go-back-n retransmission and selective retransmission.
Fragmentation is also a well-known scheme for combating the effects of fading channels. Fragmentation involves splitting large blocks of data into small frames for transmission. This has the benefit of requiring smaller buffer sizes and allowing earlier detection of errors in a block of data when each buffer is checked for errors. Fragmentation further enables retransmission of smaller frames in case of errors, and prevents one station from occupying the transmission medium too long for transmitting large blocks of data. Fragmentation is usually used together with selective retransmission for better performance.
Typical retransmission mechanisms using fragments utilize a cyclic redundancy code (CRC) to determine if a fragment is received without error. FIG. 2 shows a conventional PPDU format with multiple fragments and a CRC. Specifically, FIG. 2 shows a conventional packet format 20 with a payload 22 split into multiple payload fragments 24 for transmission at a transmitter. A CRC encoder at the transmitter then encodes k bits of information in each fragment into k+n bits, wherein n is the number of CRC bits that is placed in a corresponding CRC field 26 for each CRC fragment 24. The transmitter then transmits the k+n bits of information to a receiver through a wireless channel, wherein the receiver performs a CRC check per received fragment 24 using the CRC bits in the corresponding CRC field 26. The receiver verifies whether the k bits of information in a fragment are received correctly, wherein n bits of error can be detected.
Transmitting such fragments with CRC information from a transmitter to a receiver is often performed in a transmitter MAC layer. Similarly, performing a CRC check at the receiver is often performed at a receiver MAC layer. However, the CRC processing at the MAC layers of the transmitter and the receiver add device cost and operation complexity.